feat(tui): read Zed editor context from state db

[kitlangton]

Summary

• Adds a Zed SQLite state fallback for the TUI editor context when the websocket editor bridge is unavailable.
• Reuses the existing editor selection store so current Zed file/line context flows through James's prompt footer and synthetic context path.
• Converts Zed character offsets to 1-based editor positions and scopes polling to matching Zed workspaces.

Testing

• bun typecheck from packages/opencode
• bun run test:ci test/cli/tui/editor-context.test.ts from packages/opencode